This invention relates to communication systems, including but not limited to transmitters and receivers in radio frequency communication systems.
The basic operation and structure of a land mobile radio system is well known. Land mobile radio systems typically comprise one or more radio communication units, such as mobile and portable radios, and one or more repeaters, base stations, or base radios, that transceive information via radio frequency (RF) communication resources. These communication resources may be narrowband frequency modulated channels, TDMA (time division multiple access) slots, carrier frequencies, frequency pairs, FDM (Frequency Division Multiplexed) resources, and other RF transmission media. Land mobile radio systems may be organized as trunked communication systems, where a plurality of communication resources is allocated amongst a group of users by assigning the repeaters on a communication-by-communication basis within an RF coverage area.
A block diagram of an example communication system a known in the art is shown in FIG. 1. A communication site 101 services a coverage area 103 using a plurality of base stations, repeaters, and/or base radios 105. For the sake of simplicity, the term BRs (base radios) will be used to refer to base stations, repeaters, and/or base radios throughout this specification and claims. Within this coverage area are three communication units, a portable radio 107, and two mobile radios 109 and 111. Each of these communication units 107, 109, and 111 is presently engaged in a different call with the base site 101. The first communication unit 107 is engaged on communication channel 123 that is sourced by a first BR 113. The first mobile communication unit 109 is engaged in a call on a communication resource 125 that is sourced by a second BR 115, and the second mobile communication unit 111 is engaged in a conversation on yet another communication channel 127 that is sourced by a third BR 117 (or BR 119, e.g.).
As is known in the art, each frequency allocation, such as a TDMA slot, frequency pair, carrier frequency, FDM resource, and so forth, is given a fixed frequency band in which to operate. In today""s systems, a different BR is used to service each frequency allocation during a specific time. For example, as shown in FIG. 2, frequency allocation 1 (FA1) is serviced by BR 201 (BR1), frequency allocation 2 is sourced by BR 203 (BR2), and frequency allocations 3 through N are sourced by BRs 205, 207, 209, 211, 213, 215, and 217 (BR3 through BRN), respectively.
Presently, there is a desire to service many more communication units with a single system that covers larger geographic areas and have many different communication resources available at each site. As a consequence, more and more BRs are necessary for each system. In today""s systems, a BR is placed at each site for each different communication resource provided at the site. Hence, if there are fifteen different channels at a site, there will be fifteen different BRs at the site. For example, in a multiple site system, where there are fifteen communication resources at each of 10 sites, 150 BRs are necessary. In addition, some systems require back-up BRs to be present in case of an emergency, to ensure communications capability whenever possible. Each site is thus likely to have additional standby BRs in case of emergency. As a result, communication systems requiring so many BRs may be extremely expensive.
Accordingly, there is a need for a less expensive communication system that still provides the same amount of communication throughput over the same coverage area.